HIV Structure and Replication
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of viral structure and the function of the immune system, particularly T-helper cells. You can test your knowledge on these below.
What is a virus?
A non-living, acellular infectious particle that requires a host cell to replicate.
Describe the structure of a virus.
A virus is composed of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Viruses have attachment proteins on their surface. Some viruses also have a lipid envelope.
What is the main function of T-helper cells in the immune response?
T-helper cells activate B-cells to secrete antibodies and activate cytotoxic T-cells. They also release cytokines to stimulate phagocytes.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains HIV structure and replication or read the full notes below. Once you've gone through the whole note, try out the practice questions!
HIV Structure
What is HIV?
- HIV (Human Immunodeficiency Virus) is a retrovirus that attacks the immune system, specifically T-helper cells.
- Leads to AIDS (Acquired Immunodeficiency Syndrome), where the immune system is severely weakened, increasing susceptibility to infections.
HIV has a complex viral structure designed to infect host cells:
Lipid Envelope
- Derived from the host cell membrane.
- Contains attachment proteins that help the virus bind to T-helper cells.
Capsid
- A protein coat that surrounds the genetic material.
- Protects the viral RNA and enzymes inside.
Genetic Material (RNA)
- HIV carries two single-stranded RNA molecules instead of DNA.
- Contains genes for viral proteins.
Enzymes (Inside the Capsid)
- Reverse Transcriptase: Converts viral RNA into DNA inside the host cell.
HIV Replication Cycle
HIV cannot reproduce on its own; it hijacks host T-helper cells to replicate.
Step 1: Attachment & Entry
- HIV’s attachment proteins bind to receptors on T-helper cells.
- The viral envelope fuses with the host cell membrane, allowing HIV’s RNA and enzymes to enter the cell.
Step 2: Reverse Transcription
- Reverse transcriptase converts viral RNA into DNA.
- This step allows HIV’s genetic material to be inserted into the host cell genome.
Step 3: Integration
- Once the DNA is integrated into the host cells DNA, the viral DNA is called a provirus and remains dormant for some time.
Step 4: Transcription & Translation
- When activated, the host cell uses the viral DNA to make new viral RNA.
- Ribosomes translate this RNA into viral proteins and enzymes.
Step 5: Assembly & Release
- New HIV particles are assembled inside the host cell.
- The new viruses bud off from the host cell, taking part of its membrane to form a new lipid envelope.
- The host T-helper cell is destroyed, weakening the immune system.
Impact of HIV on the Immune System
- HIV gradually reduces the number of T-helper cells.
- Fewer T-helper cells = B-cells are not activated.
- This compromises the immune response, making the individual vulnerable to infections.
- Eventually, AIDS develops, leading to life-threatening infections and cancers.
Key Terms
- Retrovirus: A virus that converts RNA into DNA using reverse transcriptase.
- Reverse Transcriptase: An enzyme that synthesises DNA from RNA.
No answer provided.
Explain how HIV replicates inside a human cell. (6 marks)
- HIV binds to the receptor on a T-helper cell using its attachment proteins.
- The viral envelope fuses with the host cell membrane, and HIV RNA and enzymes enter the cell.
- Reverse transcriptase converts viral RNA into DNA.
- Viral DNA is incorporated into the host cells chromosomes.
- The host cell produces new HIV proteins.
- The new viruses are assembled and bud off, destroying the T helper cell.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!